Ball and socket joints have many well known applications and are tremendously successful in the market place. The joint usually comprises a spherical ball portion of a rod or other appendage that is disposed in a spherical cavity of a socket wherein the ball and socket have varying degrees of freedom to pivot and rotate relative to one another depending on the particular application. In some socket configurations, the ball is retained in the socket by a separate retaining ring that constricts an opening of the socket, or by a clamping member that retains a two-part socket assembled about the ball. Other configurations include a container that houses a separate resilient member with a cavity for receiving the ball. Multi-component sockets however have the disadvantage of requiring fabrication and assembly of the components, which increases costs and may pose reliability risks. A unitary socket which overcomes some of the disadvantages discussed above is disclosed in U.S. Pat. No. 4,993,863 to Inoue wherein resilient finger members originating near an equatorial portion of the socket have an outwardly flared skirt portion that forms an opening at one end of the socket for receiving the ball. The skirt portion and corresponding resilient finger members flex outward to permit insertion of a ball into the socket and then constrict to retain the ball in the socket. The resilient finger members however are tangentially arranged along the surface of the ball resulting in poor leverage for retaining the ball, which severely limits joint strength and therefore the scope of its practical application. U.S. Pat. No. 3,756,734 to Nicholls discusses a unitary socket having a generally cylindrical bore with opposing open end portions. Two rows of radially inwardly directed resilient projections with a concave end surface extend from the surface of the bore to define a spherical ball seating or socket between the rows. The resilient projections flex radially outward to permit insertion of the ball into the socket through the opening at either end portion and then constrict the opening to retain the ball in the socket. The rows of resilient projections, though more secure than the tangential resilient finger members discussed above, provide little contact surface area between the ball and the socket and therefore do not provide a very strong joint, particularly where ball forces are along the axial dimension of the bore toward the open end portions. These open-ended joints therefore are limited to applications where the ball forces are directed substantially radially outward toward the walls of the cylindrical bore whereas ball forces directed substantially along the axis of the bore toward either open end portion of the socket are likely to result in separation of the ball from the socket for lack of sufficient contact surface area between the ball and the resilient projections.
Another problem sometimes arises with prior art ball and socket joints during assembly of the joint, which is often performed by an automated system that inserts several balls into corresponding sockets in a single operation. In the assembly of ball and socket joints used for mounting automotive head lamps for example the sockets are fixed in a stationary mount while the balls are retained on a common moving member that simultaneously inserts or snaps the balls into the socket during an insertion step. In practice however the common moving member does not retain the balls in accurate alignment before the insertion step, which results in improper spacing between the ball and corresponding socket prior to assembly. When the pre-assembly spacing between the ball and socket is too large, the moving member may not fully insert the ball into the socket, and when the pre-assembly spacing between ball and socket is too small, the moving member may insert the ball too far into the socket, which results in damage or destruction to the socket. Damage to the socket due to excessive assembly force is particularly likely to occur in sockets that provide a insufficient contact surface area between the ball and socket, which is indicative of inadequate ball and socket joint strength. In the unitary socket of the type discussed in U.S. Pat. No. 4,993,863 to Inoue, excessive force on the ball during assembly or operation is likely to result in the ball being disposed into one side of the socket and out the other side of the socket due to lack of an adequately closed end portion for retaining the ball.
Ball and socket joint applications often require a tight fitting joint with little or no play between the ball and socket joint, wherein the components must be manufactured to close tolerances resulting in increased costs. Many spherical ball portions however are not at all spherical, but have irregular shapes and sizes usually resulting from the fabrication process. Balls formed by molding processes for example often have a flat surface, and balls formed by forging processes often have a flat surface and may vary in size and shape. Other balls are intentionally formed with a flat surface having a tool engagement slot or key for receiving a drive means such as a hex head, which is useful for assembly of an appendage extending from the ball. The irregularities in the shape and size of the ball and socket however result in a sloppy or loose fitting joint, which may have adverse consequences in a particular application. Automobile head lamp housings for example are usually adjustably mounted on a plurality of rods with ball portions seated in corresponding sockets mounted on the frame or other structure of the automobile. A loose ball and socket joint in this application results in unwanted vibration of the head lamp and a shimmering head light, which is annoying and possibly dangerous to motorists. Efforts have been made to securely retain the ball in the socket in other applications, but not without undue expense. U.S. Pat. No. 4,136,617 to Nemoto for example discusses a socket with a separate ball seat member biased into contact with the ball by a separate resilient spring member. As discussed above however this system has the disadvantage that it requires costly fabrication and assembly of its separate components.